Norovirus Infection

Description

Noroviruses (also referred to as "Norwalk-like viruses," Norwalk viruses, human caliciviruses, and small round-structured viruses) are a common cause of acute gastroenteritis worldwide.

Norovirus infection presents as vomiting and diarrhoea and usually occurs in large outbreaks propagated by faecal-oral transmission via contaminated food or water or by direct person-to-person contact. Evidence also suggests that norovirus can be transmitted via aerosolized vomit and contact with contaminated objects.

Occurrence

In the United States, norovirus infections are estimated to cause 23 million illnesses a year. Seroprevalence studies in the Amazon, southern Africa, Mexico, Chile, and Canada have shown that norovirus infections are common throughout the world. Infection can occur year-round.

Risk to Travellers

Travellers of all ages are potentially at risk for norovirus infection, and previous infection does not reliably result in subsequent immunity.

Risk of infection is present anywhere where food is prepared unhygienically or drinking water is inadequately treated. Of particular risk are "ready-to-eat" cold foods, such as sandwiches and salads. Raw shellfish, especially oysters, are also a frequent source of infection. (Please see the "Risks from Food and Drink" section for additional information.)

Norovirus infection also has been associated with large outbreaks of gastroenteritis in various settings where persons living in close quarters, such as hotels, cruise ships, and camps, can easily infect each other over several days. Inapparent viral contamination of inanimate objects during outbreaks can also act as a source of infection.

Clinical Presentation

Infected persons usually have acute-onset, violent vomiting and nonbloody diarrhoea after an incubation period of 24-48 hours. Other symptoms include abdominal cramps, nausea, and occasionally a low-grade fever. Illness is generally self-limited, and full recovery can be expected in 1-4 days. In some cases, dehydration, especially in those who are very young or elderly, may require medical attention. (For infants, please refer to Table 8-1 for Assessment of Dehydration Levels for Infants.)

Prevention

No vaccines are available. Noroviruses are very common and highly contagious, but the risk of infection can be minimized by frequent and proper handwashing and avoidance of possibly contaminated food and water.

In addition to handwashing, measures to prevent transmission of noroviruses between persons travelling together include careful clean-up of faecal material or vomit and disinfection of contaminated surfaces with domestic bleach (at least a 1:50 solution of bleach and water). Soiled articles of clothing should be washed promptly and thoroughly and machine-dried at high heat. Confinement of ill persons to help prevent the spread of noroviruses has occasionally been implemented on cruise ships.

Treatment

No antiviral medication is available for treating norovirus infection. Supportive care, such as rest and oral rehydration, is the mainstay of management. (See Table 4-19, Composition of World Health Organization Oral Rehydration Solution (ORS) for Diarrhoeal Illness.)

Bibliography
  • Bresee JS, Widdowson M-A, Monroe SS, Glass RI. Foodborne viral gastroenteritis: challenges and opportunities. Clin Infect Dis 2002;35: 748-53.
  • CDC. Norovirus activity, United States, 2002. MMWR Morbid Mortal Wkly Rep 2003; 52:41-5.
  • CDC. Norwalk-like viruses: public health consequences and outbreak management. MMWR Morbid Mortal Wkly Rep 2001;50: (RR-9).
  • CDC. Outbreaks of gastroenteritis associated with noroviruses on cruise ships—United States, 2002. MMWR Morbid Mortal Wkly Rep 2002; l51: 1112-5.
  • Mead PS, Slutsker L, Dietz V, et al. Food-related illness and death in the United States. Emerg Infect Dis 1999;5:607-25

- Eileen Lau and Marc-Alain Widdowson

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